1. Field of the Invention
The present invention relates to a scroll compressor that compresses air, and more particularly to an oil-free scroll compressor in which water is injected into a compression chamber instead of oil.
2. Description of the Related Art
An oil-free compressor in which oil (lubricating oil) is not injected into a compression chamber is known as one example of compressors that compress air. The oil-free compressor is essential in the field such as food industry and semiconductor manufacturing processes in which clean compressed air that does not contain oil is required. The oil-free compressor, however, has a lower compression efficiency than an oil feeding compressor that requires oil to be injected into a compression chamber. In addition, the oil-free compressor needs to be subjected to maintenance at a shorter interval compared with the oil feeding compressor. Thus, the oil-free compressor is disadvantageous in terms of performance and reliability. To address such problems, an oil-free screw compressor has been put into practical use, in which water is injected into a compression chamber for high cooling and sealing effects.
Scroll compressors are advantageous in that noise and vibration are low. For example, JP-08-128395-A discloses an oil-free scroll compressor in which water is injected into compression chambers. Such an oil-free scroll compressor is of double scroll type. This type of oil-free scroll compressor includes an orbiting scroll member and two fixed scroll members. The orbiting scroll member has two substantially spiral wraps on both surfaces thereof. One of the fixed scroll members is located on one side of the oil-free scroll compressor. The fixed scroll member has a substantially spiral wrap provided on one surface thereof and corresponding to one of the substantially spiral wraps of the orbiting scroll member. The other of the fixed scroll members is located on the other side of the oil-free scroll compressor. The other fixed scroll member has a substantially spiral wrap provided on one surface thereof and corresponding to the other of the substantially spiral wraps of the orbiting scroll member. The oil-free scroll compressor also has a water injection system. The water injection system injects water through a hole provided in one of the fixed scroll members into a compression chamber that is located on one side of the orbiting scroll member, and injects water through a hole provided in the other of the fixed scroll members into another compression chamber that is located on the other side of the orbiting scroll member. The water injection system has a liquid tank, a pump device, a tube and valve devices. The liquid tank stores water and is connected with the pump device. The tube is divided into two tubes on a discharge side of the pump device. The one of the divided tubes communicates with the hole provided in the one of the fixed scroll members, while the other of the divided tubes communicates with the hole provided in the other of the fixed scroll members. One of the valve devices is installed to the one of the divided tubes, while the other of the valve devices is installed to the other of the divided tubes.